1. Field of the Invention
The invention relates to inlet manifolds for delivering combustion gases to radial-inflow turbines.
2. Description of the Prior Art
In conventional radial in-flow gas turbines, combustion gases are generated in one or more can-type combustors and then fed to a scroll or toroidal-shaped manifold for distribution to an annular turbine inlet guide vane assembly which imparts angular momentum to the hot gases before it enters the turbine blades. Double-walled inlet manifolds are known such as where an inner wall channels the hot combustion gases from the combustors to the turbine inlet nozzle assembly and where a surrounding wall defines a flow passage for a coolant gas to cool the inner wall. It is also known to use compressed air as the coolant gas in such constructions and to channel the heated compressed air to the combustors to be utilized as combustion air and thereby to recover heat values. See e.g. U.S. Pat. No. 2,801,519 (Wood).
Although early double-walled inlet manifolds were essentially entirely convection cooled, that is, film cooling was not utilized, these applications involved relatively low temperature turbine applications where material temperature/strength limits were not in jeopardy. For conventional high temperature turbine applications (i.e. T comb. exit 1100.degree.-1200.degree. C.), film cooling is employed wherein some of the coolant gas is bled from the coolant gas space into the combustion gas space of the manifold to flow along the inner wall surface in much the same manner as conventional can combustors are cooled.
However, film cooling degrades the performance of the turbine by increasing the peak-to-average combustion gas temperature ratio of the gas exiting the manifold and entering the turbine. Thus, an inlet manifold cooled by convection only would be highly desirable for high temperature turbine applications. Also, for high performance/weight applications where the coolant gas used is compressed air intended for utilization as combustion air, it is desirable to have an inlet manifold which has a minimum coolant gas pressure drop while also minimizing the size of the inlet manifold cooling structure. In early convection cooled double-walled inlet manifolds, a counter flow design was employed using relatively large distances between inner and outer manifold walls to reduce pressure drop but this necessarily increased the size and thus the weight of the unit.